1. Field
Embodiments of the invention relates to a proton conductive polymer which can be preferably used in fuel cell and alkaline electrolysis industry and a fuel cell comprising an electrolyte membrane containing the proton conductive polymer.
2. Description of the Related Art
A fuel cell performs electrochemical reaction of hydrogen with oxygen to generate electricity and thus has been noted as a clean electricity-generating device. As such a fuel cell there has been heretofore known a solid polymer electrolyte type fuel cell that uses hydrogen gas as a fuel. The solid polymer electrolyte membrane to be used in this solid polymer electrolyte type fuel cell is disclosed in, e.g., JP-A-2002-110174 and JP-A-2003-36864.
JP-A-2002-110174 discloses that a solid polymer electrolyte membrane made of an aromatic hydrocarbon-based polymer compound containing a sulfoalkyl group in its side chains exhibits an enhanced durability that improves the output characteristics of solid polymer electrolyte type fuel cell. On the other hand, JP-A-2003-36864 discloses a solid polymer electrolyte membrane composed of a main chain formed by a copolymer of fluorocarbon-based vinyl monomer with hydrocarbon-based vinyl monomer and a hydrocarbon-based side chain having a sulfonic acid group wherein the hydrocarbon-based side chain has α-methylstyrene group incorporated therein, thereby inhibiting the oxidative deterioration of solid polymer electrolyte membrane.
A direct methanol type fuel cell (DMFC) that operates by supplying methanol into the anode thereof while being left unreformed has been under study. This direct methanol type fuel cell requires no reformer and thus can be drastically reduced in its weight and compacted. Therefore, the direct methanol type fuel cell has been expected as a portable fuel cell.
As the proton conductive membrane to be incorporated in such a direct methanol type fuel cell there has been widely used a perfluorosulfonic acid polymer membrane as disclosed in JP-A-2002-313366. However, this perfluorosulfonic acid polymer membrane undergoes a great methanol crossover phenomenon. Further, this perfluorosulfonic acid polymer membrane leaves something to be desired in protonic conductivity. Accordingly, membrane-electrode assemblies (MEA) formed by this perfluorosulfonic acid polymer membrane cannot provide a sufficient electricity-generating efficiency.